1. Field of the Invention
The present invention relates to an on-vehicle display unit that projects an image, which is displayed on a display disposed in a dashboard of a vehicle, on a windscreen or an auxiliary screen. The image is superimposed over the foreground which can be seen through the windscreen or the auxiliary screen.
2. Related Art
Such a on-vehicle display unit, which is called as a head-up display, allows a driver to see additional information necessary for an operation of the vehicle together with the foreground without a larger change of a sight line of the driver.
The on-vehicle display unit can compensate eye positions that are variable according to a physique or a position of the driver. Such on-vehicle display units are disclosed in Japanese Patent Applications Laid-open No. 5-229366, No. 6-48218, NO. 6-144082, and No. 7-144557.
In the prior arts, an image emitted from a display is projected on a windscreen or an auxiliary screen by way of a reflecting mirror. The mirror has an inclination angle which is variable to adjust a vertical position of the image on a windscreen or an auxiliary screen.
However, the change of the inclination angle of the mirror varies an incidence angle of light from the mirror on the windscreen or the auxiliary screen. Thereby, a reflection angle of the light on the windscreen varies. Thus, the inclination angle of the mirror should be varied delicately according to a vertical position of an eye so that the image is superimposed over the foreground.
By the way, a driver""s sight line is directed generally to a point which is 10 to 20 meter ahead of a vehicle, although the point varies with the speed of the vehicle. The distance from the eye position to the sight point is considerably larger than the distance between the eye position and the windscreen, so that different vertical positions of the driver""s eye cause almost no change of the angle of the driver""s sight line relative to a roadway.
Thus, when the eye position is changed, the vertical shift distance of the image on the windscreen is preferably the same as the vertical shift distance of the eye position.
However, as described above, in the prior arts, the vertical shift of the image on the windscreen should be delicately adjusted relative to the vertical shift of the eye position. The change of the mirror inclination angle causes a shift of the image on the windscreen from the driver""s sight line directed to an appropriate point of the foreground. This shows that the prior arts are susceptible to improvement.
Another of such on-vehicle display units is also disclosed in Japanese Patent Application Laid-open No. 7-257228. The on-vehicle display unit adjusts the vertical position of additional information on a windscreen to coincide with a present sight line of a driver. Furthermore, Japanese Patent Applications Laid-open No. 6-115381 and No. 9-185012 each disclose one of such on-vehicle display units which corrects the vertical position of additional information on a windscreen according to a vehicle""s speed.
However, there has been no proposal which can keep a driver""s sight line directed an appropriate point of the foreground when the vertical position of the driver""s eye varies.
Moreover, another improvement is desired in the prior arts. The vertical adjustment of the image on the windscreen by changing the inclination angle of the mirror causes light reflected from the mirror to pass through different points of the dashboard. Thus, the dashboard should be provided with a window through which the variable reflected light can pass.
This makes the dashboard window larger, which requires an adequate measure for preventing entry of dust and contaminants into the dashboard.
In view of the aforementioned situation, an object of the invention is to provide an on-vehicle display unit which can see an image reflected from a windscreen of a vehicle together with the foreground visible through the windscreen. The on-vehicle display unit requires little change of a driver""s sight line when the driver sees the image and the foreground in a superimposed relationship thereof, even when eye positions of the driver vary vertically according to a physique or a position of the driver.
Another object of the invention is to provide another on-vehicle display unit which can see an image reflected from a windscreen of a vehicle by way of a reflecting mirror together with the foreground visible through the windscreen. The reflecting mirror has an inclination angle variable with a driver""s eye position which vertically changes according to a physique or a position of the driver. The on-vehicle display unit has a window defined in a dashboard for passing light reflected by the mirror, the window being able to appropriately prevent entry of dust and contaminants.
For achieving the first object of the invention, a first aspect of the invention is an on-vehicle display unit for projecting an image on a screen, the image displayed on a display in a dashboard of a vehicle, the screen disposed above the dashboard and extended diagonally in a vertical plane relative to a longitudinal direction of the vehicle, the screen being transparent so that the foreground is visible through the screen with the image projected on the screen being superimposed over the foreground. The on-vehicle display unit includes a reflecting mirror disposed in the dashboard for reflecting light emitted from the image displayed on the display toward the screen. The reflecting mirror can be located at any of different positions in a longitudinal direction of the vehicle.
Thus, when the longitudinal location of the mirror is changed in the dashboard, the image projected on the screen moves vertically with no change of an incidence angle of light reflected by the mirror toward the screen.
Hence, the on-vehicle display unit requires little change of a driver""s sight line when the driver sees both the image and the foreground, even when eye positions of the driver vary vertically according to a physique or a position of the driver.
Preferably, the on-vehicle display unit further has a transfer mechanism supporting the mirror such that the mirror is movable in the longitudinal direction, wherein the transfer mechanism can locate the mirror at any of the different positions.
Thus, the longitudinal transfer of the mirror supported by the transfer mechanism can easily change the longitudinal position of the mirror in the dashboard.
Optionally, the screen has a curved surface with different inclination angles relative to the longitudinal direction, and the transfer mechanism has an inclination angle adjusting device for changing the inclination angle of the mirror relative to the longitudinal direction in conformity with the inclination angle of the curved screen surface on which the image is projected when the mirror is moved in the longitudinal direction.
Thereby, even when the screen has a curved surface with different inclination angles to the longitudinal direction, light delivered from the screen to a driver""s eye keeps a substantially constant incidence angle to a longitudinal direction of the vehicle.
Preferably, the on-vehicle display includes a plurality of the mirrors and a reflecting mirror moving mechanism for selectively moving each of the mirrors forward and backward for reflecting light emitted from the image displayed on the display such that each of the mirrors can be located at each of the different positions in the longitudinal direction of the vehicle.
Thereby, the mirror moving mechanism can selectively move each of the mirrors forward and backward for reflecting light emitted from the image displayed on the display. This can easily change the longitudinal positions of the mirrors in the dashboard.
Optionally, the screen has a curved surface with different inclination angles relative to the longitudinal direction, and each of the mirrors has a predetermined inclination angle relative to the longitudinal direction according to the inclination angle of the screen surface on which the image is projected.
Thus, even when the screen has a curved surface with different inclination angles to the longitudinal direction, light reflected by the screen toward a driver""s eye has a constant angle relative to the longitudinal direction of the vehicle. Hence, the on-vehicle display unit requires little change of a driver""s sight line when the driver sees both the image and the foreground, even when eye positions of the driver vary vertically according to a physique or a position of the driver.
Preferably, the on-vehicle display further includes a second reflecting element spaced from the display in a longitudinal direction of the vehicle, and the mirror is a semi-transparent mirror which can pass partially light emitted from the display toward the second reflecting element, the second reflecting element reflecting the light toward the semi-transparent mirror such that the light is reflected toward the screen by the semi-transparent mirror.
Thus, the optical path from the display to the screen by way of both the second reflecting element and the mirror is much longer than the distance between the display and the screen. Thereby, a driver can easily focus on the foreground and the image emitted from the display.
Preferably, the on-vehicle display unit further includes an image magnifying optical element disposed in the dashboard for magnifying the image which is delivered to the semi-transparent mirror.
Even when the image is visible by way of the semi-transparent mirror, the reflecting element, and the screen for providing a lengthened focus distance, the image magnifying optical element can keep the image in an appropriate size for recognition.
Preferably, the image magnifying optical element is a Fresnel lens having a flat surface at one side thereof and a Fresnel surface at the other side thereof, the flat surface facing the second reflecting element in an optical axis direction of the image emitted from the display.
The Fresnel lens is disposed between the reflecting element and the semi-transparent mirror such that the Fresnel lens is in no interference relationship with the longitudinal movement of the semi-transparent mirror. This enables the image magnification as well as an elongated focusing distance of the image, which is better for the driver to see the superimposed image and the foreground.
Preferably, the on-vehicle display unit further includes a window disposed on an upper surface of the dashboard and a transfer mechanism for moving the window in a longitudinal direction of the vehicle, the window partially allowing light of the image reflected from the mirror to pass through the window toward the screen.
Thus, the longitudinal position of the window is adjusted according to the longitudinal position of the mirror. Thereby, the window can have a minimum size so that the entry of contaminants and undesirable eternal rays into the dashboard is minimized to surely project the image toward the screen.
Preferably, the on-vehicle display unit further includes a window closing mechanism for closing and opening the window.
Thus, the window closing mechanism can selectively close the window when the image of the display is not required to be projected on the screen. Thereby, the entry of contaminants and undesirable external rays into the dashboard is minimized.
A second aspect of the invention is an on-vehicle display unit for projecting an image on a screen by way of a reflecting mirror, the image displayed on a display in a dashboard of a vehicle, the screen disposed above the dashboard, the mirror being movable in the dashboard so that the image projected on the screen is movable. The on-vehicle display unit includes:
a window disposed on an upper surface of the dashboard, the window partially allowing light of the image reflected from the mirror to pass through the window toward the screen and
a transfer mechanism for moving the window along the upper surface of the dashboard according to a variable position of the image projected on the screen.
The inclination angle and longitudinal position of the mirror are adjusted when eye positions vary vertically according to a physique or a position of the driver. With the adjustment of the mirror, the transfer mechanism moves the window along the upper surface of the dashboard. Thereby, the window can have a minimum size so that the entry of dust and contaminants into the dashboard is minimized.
Preferably, the mirror is inclined by a predetermined angle relative to a central optical axis of the image emitted from the display, the mirror being movable in the dashboard so as to align with the central optical axis, and the transfer mechanism can move the window to align the window with the central optical axis.
Thus, the transfer mechanism moves the window to face the optical axis so that the window is surely positioned to cooperate with the mirror.
Preferably, the mirror is supported by a holder, and the window is defined in a cover movably supported on the upper surface of the dashboard to align with the optical axis, the cover attached to the holder through a connection member.
Thus, the window moves in response to the movement of the mirror so that the window is always positioned to appropriately cooperate with the mirror.
Preferably, the window is defined in a cover movable on the upper surface of the dashboard in conformity with a variable position of the image on the screen, and the cover has a plurality of bar plates which are joined to one another along a folding line intersecting with a movement direction of the cover, each bar plate being foldable along the folding line.
Thus, even when the cover moves on a curbed surface of the dashboard, the cover consisting of the foldable plate bars can overlay along the curved surface.
Preferably, the on-vehicle display unit further includes a closing mechanism for closing and opening the window.
Thus, the window closing mechanism can selectively close the window when the image of the display is not desired to be projected on the screen. Thereby, the entry of contaminants and undesirable external rays into the dashboard is minimized.
Preferably, the window is covered by a transparent cover having a surface facing upward from the dashboard, the surface being treated with by a reflection limiting process.
Thus, the cover prevents the entry of contaminants into the dashboard and also prevents an undesirable reflection of external rays on the cover not to be glare for the driver.
Preferably, the on-vehicle display unit further includes a transparent cover for covering the window and a shade defined at a periphery of the window, the shade raised from the upper surface of the dashboard, the cover having a surface facing upward above the dashboard, the surface being able to reflect light projected on the surface toward the shade.
Thus, the cover prevents the entry of contaminants into the dashboard, and the shade prevents the undesirable reflection of rays from the cover to eliminate glare for the driver.